1. Field of the Invention
The invention relates to an optical color sensor. In particular, the invention relates to an apparatus utilizing the optical color sensor for inspecting a color print on a printed product such as a news paper.
2. Description of Related Art
There has been proposed an apparatus for inspecting a color print on a printed product, as disclosed in Japanese Laid-Open Patent Publication No. 156,080 of 1997. The printed product is color printed with four color inks of yellow, cyan, magenta and black. In this connection, the apparatus includes two light sources one of which comprises blue LEDs for directing a blue light onto the printed product to directly illuminate the printed product with the blue light. The other light source comprises red LEDs for directing a red light onto the printed product to directly illuminate the printed product with the red light. The apparatus further includes a photo diode array for receiving and detecting a reflected light reflected from the printed product. The light sources are selectively and alternately energized by a switching circuit to read out the color print on the printed product. For example, the blue LEDs are energized by the switching circuit to direct the blue light onto the printed product. The photo diode array receives and detects the reflected light reflected from the printed product to read out and inspect the color print of yellow, magenta and black. The red LEDs are then energized to direct the red light onto the printed product. The photo diode array receives and detects the reflected light reflected from the printed product to read out and inspect the color print of cyan and black.
By the way, it is desired to achieve a more and more high productivity without lowering a quality, in the color printing industry. Accordingly, it is required to quickly and reliably inspect the color print of each color and determine it to be good or no good. However, in the apparatus, the light sources have to be selectively and alternately energized to read out and inspect the color print of each color. A switching time is required whenever the light sources are selectively and alternately energized. It also takes a certain time to provide a stable amount of light after switching. Accordingly, the apparatus can not quickly and reliably inspect the color print of each color to meet the requirement of high productivity and high quality.
It is therefore an object of the invention to provide a new and improved optical color sensor, to overcome the above problem.
Other object of the invention is to provide an apparatus utilizing the optical color sensor for inspecting a color print on a printed product.
Other object of the invention is to quickly and reliably inspect the color print of each color and determine it to be good or no good.
3. Summary of the Invention
According to the invention, there is provided an optical color sensor. The optical color sensor comprises a light source which comprises white LEDs for directing a white light onto a product to be inspected, to directly illuminate the product with the white light and generate a reflected light reflected from the product. The optical color sensor further comprises first photo detecting element means spaced from the product. A blue filter is interposed between the first photo detecting element means and the product so that the first photo detecting element means can receive and detect the reflected light passing through the blue filter. The optical color sensor further comprises second photo detecting element means spaced from the product. A red filter is interposed between the second photo detecting element means and the product so that the second photo detecting element means can receive and detect the reflected light passing through the red filter. The first and second photo detecting element means are arranged to receive and detect the reflected light reflected from the product at substantially the same position in a region onto which the white LEDs direct the white light to directly illuminate the product.
In a preferred embodiment, the blue filter causes the reflected light having a wave length of nearly 450 nm to pass therethrough, while the red filter causes the reflected light having a wave length of nearly 650 nm to pass therethrough.
The white LEDs are disposed between the first and second photo detecting element means.
There is also provided an apparatus for inspecting a color print on a printed product which is fed in a direction. The apparatus comprises a color print reading head which comprises a plurality of optical color sensors arranged in line in a direction vertical to the feeding direction of the printed product for reading out the color print on the printed product. The optical color sensors each comprises a light source which comprises white LEDs for directing a white light onto the printed product, to directly illuminate the printed product with the white light and generate a reflected light reflected from the printed product. The optical color sensor further comprises first photo detecting element means spaced from the printed product. A blue filter is interposed between the first photo detecting element means and the printed product so that the first photo detecting element means can receive and detect the reflected light passing through the blue filter to read out the color print on the printed product. The optical color sensor further comprises second photo detecting element means spaced from the printed product. A red filter is interposed between the second photo detecting element means and the printed product so that the second photo detecting element means can receive and detect the reflected light passing through the red filter to read out the color print on the printed product. The first and second photo detecting element means are arranged to receive and detect the reflected light reflected from the printed product at substantially the same position in a region onto which the white LEDs direct the white light to directly illuminate the printed product.
The apparatus may further comprise reference data memory means for storing the read out data transmitted from the reading head as reference data. The apparatus may further comprise color print data memory means for storing the read out data transmitted from the reading head as color print data. The apparatus may further comprise comparing and evaluating means for comparing the color print data transmitted from the color print data memory means with the reference data transmitted from the reference data memory means to evaluate the difference between the color print data and the reference data obtained by the reflected light passing through the blue filters of the optical color sensors, as a first evaluated value, and evaluate the difference between the color print data and the reference data obtained by the reflected light passing through the red filters of the optical color sensors, as a second evaluated value. The apparatus may further comprise first flag establishing means for comparing the first evaluated value with a warning tolerance predetermined with respect to the reference data for each color to establish a good or no good flag for each color, and comparing the first evaluated value with a warning reference value which is the warning tolerance multiplied by a correction value for each color, to establish a good or no good flag for each color. The apparatus may further comprise second flag establishing means for comparing the second evaluated value with a warning tolerance predetermined with respect to the reference data for each color to establish a good or no good flag for each color. The apparatus may further comprise determining means for determining the color print of each color to be good or no good in accordance with the result of comparison of the second evaluated value with the warning tolerance and the good or no good flags to generate an output signal indicating the determination.